A transmission apparatus includes an active programmable device; a standby programmable device upgrading the version; an external memory part that includes a table memory and a main signal memory and that is shared between the two programmable devices; and a switching part that selects either of the main signals processed by the two programmable devices to transmit the selected main signal to an output path. The active programmable device is capable of processing the main signals in parallel with the standby programmable device and receives a notification of completion of the version upgrade from the standby programmable device to issue an instruction to start switching to the standby programmable device. The standby programmable device uses the table memory and the main signal memory updated by the active programmable device to process the main signals in response to the instruction to start the switching.